The present invention relates to a printing apparatus and an image data processing method of the printing apparatus, and more particularly, to image data processing in a printing apparatus which performs printing by using a full-line type printhead.
A printing apparatus which performs printing based on information on desired characters, images and the like on a sheet-type print medium such as print paper or a film is widely used as an information output device in a word processor, a personal computer, a facsimile machine and the like. Further, a printing apparatus which performs high-speed printing using a so-called full-line type printhead while conveying a print medium is known as this type of apparatus. The printhead has a printing area, corresponding to the width of printing area of print medium such as a print sheet, in a direction vertical to a transfer direction of the print medium.
An ink-jet type line head, an electrophotographic LED line head and the like are known as such full-line type printheads of the printing apparatus. A color page printer using plural such printheads, an electrophotographic page printer using laser light and the like are known.
Conventionally well-known problems include, when a color image is formed by using plural full-line type printheads, printing positions of respective colors are shifted due to attachment errors and the like of the respective printheads. As an example, an electrophotographic color page printer will be described. This color printer has four types of printheads, a black printhead, a cyan printhead, a magenta printhead and a yellow printhead. Upon printing with these printheads, registration adjustment is necessary.
Japanese Published Unexamined Patent Application No. Hei 07-115553 discloses such registration adjustment method. In this method, registration adjustment is made in printing by dividing image data into arbitrary image blocks, then in reading, time-divisionally changing pixel reading positions in each image block.
However, in the block-based processing as disclosed in the above publication, image data cannot be written into a memory before all the data for at least one pixel block is prepared. Accordingly, in a line-sequential image processing system to process image data continuous in a main scanning direction (raster data), the amount of data in the main scanning direction increases, and a memory capacity in proportion to the amount of data is required.
Especially, in data coding in pixel block units, it is necessary to store all the data for 1 pixel block. Further, as described in Japanese Published Unexamined Patent Application No. Hei 07-115553, upon data coding, if some data drop due to compression/expansion is allowable, coding to a fixed length code is possible; however, generally, in lossless coding in which data drop due to compression/expansion is not allowable, if a predetermined amount of pixel block is compressed, the amount of data is not fixed, and the amount of coded information differs in correspondence with the data status.
Accordingly, if conversion to fixed length code cannot be performed, the memory management method described in the above publication cannot be used.
The present invention has been made in consideration of the above situation, and can provide a printing apparatus capable of image printing in correspondence with an attachment angle of a full-line type printhead and capable of automatic registration adjustment when using plural printheads, and an image data processing method for the printing apparatus.
According to the present invention, the foregoing object is attained by providing a printing apparatus which performs printing by using a full-line type printhead having a printing area corresponding to a width of a printing area of a print medium, comprising: detection means, for detecting a relative angle of the printhead to a transfer direction of the print medium; division means for dividing image data, received in raster format, into plural pixel blocks; storage means for storing the divided pixel blocks; determination means for determining an order of reading/writing of the pixel blocks for the storage means, based on the relative angle detected by the detection means; and control means for performing the reading/writing of the pixel blocks for the storage means in the order determined by the determination means.
Further, the foregoing object is attained by providing an image data processing method for a printing apparatus which performs printing by using a full-line type printhead having a printing area corresponding to a width of a printing area of a print medium, comprising: a detection step of detecting a relative angle of the printhead to a transfer direction of the print medium; a division step of dividing image data, received in raster format, into plural pixel blocks; a storage step of storing the divided pixel blocks into storage means; a determination step of determining an order of reading/writing of the pixel blocks for the storage means, based on the relative angle detected at the detection step; and a control step of performing the reading/writing of the pixel blocks for the storage means in the order determined at the determination step.
That is, the relative angle of printhead with respect to the print-medium transfer direction is detected, then raster image data is divided into plural blocks and stored, then the order to read the stored plural blocks is determined in accordance with the detected relative angle, and the read data is transmitted to the printhead.
In this construction, as the pixel block data is transmitted to the printhead in the order corresponding to the attachment angle of the printhead, image data can be print-outputted always at the same angle regardless of the attachment angle of the printhead. Accordingly, upon color printing by using plural printheads, the influence of attachment errors, of the respective printheads can be reduced and the registration adjustment can be facilitated. Further, as the memory used as the storage means can be shared among the plural printheads, and various compression/expansion methods can be used in correspondence with image data type, the memory can be effectively used and the capacity can be reduced.
The present invention is applicable to a printing apparatus having plural printheads, wherein the respective printheads use different-color printing materials in color printing.
In this case, it is preferable that the storage means can be commonly used among the plural printheads.
Further, as the detection means, plural readers arrayed along the transfer direction of the print medium can be used, and image data corresponding to 1 raster printed by the printhead is read by the respective readers so as to detect the relative angle.
Further, if it is arranged such that the division means includes compression means for compressing image data, and the transmission means includes expansion means for expanding compressed image data, it is preferable that various compression/expansion methods can be used in accordance with image data type.
Preferably, the printhead is an ink-jet printhead which performs printing by discharging ink utilizing thermal energy or the like.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.